My users have several external imap-accounts included in their imap-accounts. All have a similar problem : the external accounts are queried on an irregular base.

Even mails that arrived in the boxes several days ago are not shown unless the users presses the "get mail"-button for this account. Even then frequently not all are fetched. Some mails only appear after pressing this button several times (its true - I've the same problem in my box and I wait between pressing the button), The problem affects mail in the inbox and the subboxes of the external account.

This is very annoying of course. And in account-settings there is no setup like "query external account every x minutes"

Most (all?) of the reported cases affect external zimbra-accounts.

That means: users include other zimbra-accounts on the same zimbra-server as external account. This makes perfectly sense: every user has its own mailbox and then there are mailboxes that are shared by serveral users. Easiest way to use this mailboxes are to include them as external imap-account. Much easier than using zimbra-internal share-mechanism especially when the account has a number of subfolders.